β-Galactosidase and production thereof

Abstract

A new beta -galactosidase is now provided which is highly effective to digest lactose and stable at acidic pH values and thermally stable. The beta -galactosidase is produced by Penicillium multicolor in high yield and is isolated from the culture medium of this microorganism in an inexpensive and easy way.

What we claim is: 
     
       1. A powdery β-galactosidase isolated from the culture medium of Penicillium multicolor and having the following characteristics: a. having a relative β-galactosidase activity of 224% for o-nitrophenyl-β-D-galactopyranoside and of 186% for p-nitrophenyl-β-D-galactopyranoside when assumed that the relative β-galactosidase activity is 100% for lactose;   b. having a molecular weight of about 120,000 as determined according to the gel-filtration method;   c. being active at pH of 2.5 to 7, the optimum pH being at 4.5;   d. said β-galactosidase activity being lost by heating at pH 6 and at 75° C. for 15 minutes, the optimum temperature being at 55° C.;   e. said β-galactosidase activity being stable in a pH range of 2.5 to 8.0 when standing at 4° C. for 24 hours;   f. said β-galactosidase activity being stable at 100% at 60° C. and reduced to 60% at 65° C., to 25% at 70° C. and to 0% at 75° C. when standing at pH 6 for 15 minutes;   g. said β-galactosidase activity being inhibited by about 20% by the presence of mercuric ion (Hg ++ ) but being not substantially inhibited by the presence of ferrous ion (Fe ++ ) and cupric ion (Cu ++ ) at a metal ion concentration of 10 -3  M; and   h. having an iso-electric point of 5.37 when measured according to an electrophoresis method.   
     
     
       2. A β-galactosidase according to claim 1, obtained from Penicillium multicolor KU-O-132 identified as FERM-P 4375. 
     
     
       3. A β-galactosidase according to claim 1, in the form of a powder having a relative β-galactosidase activity of about 34,800 units/g. 
     
     
       4. A process for the production of a β-galactosidase, which comprises: a. cultivating a strain of Penicillium multicolor in a culture medium containing assimilable carbon and nitrogen sources to produce and accumulate the β-galactosidase in the medium, and   b. then isolating the β-galactosidase from the medium.   
     
     
       5. A process according to claim 4 in which liquid cultivation of Penicillium multicolor is conducted at a temperature of 10°-40° C. and at a pH of 4-9 for a period of 1 to 8 days under aerobic conditions. 
     
     
       6. A process according to claim 4 which comprises: a. cultivating Penicillium multicolor in a culture medium containing bran as assimilable nitrogen source to produce and accumulate the β-galactosidase in the medium,   b. extracting the medium with water to give an aqueous extract solution of the enzyme,   c. precipitating the enzyme from the extract by addition of acetone; and   d. drying the resulting precipitate.   
     
     
       7. A process according to claim 4 which comprises: a. cultivating Penicillium multicolor in a liquid culture medium containing assimilable nitrogen and carbon sources under aerobic conditions to produce and accumulate the enzyme in the liquid medium,   b. filtrating the liquid culture broth to remove solid matter,   c. concentrating the clear filtrate obtained,   d. precipitating the enzyme from the concentrated filtrate by the addition of acetone, and   e. drying the resulting precipitate.